Problem: $ E = \left[\begin{array}{rrrr}-1 & -2 & 4 & 2 \\ 2 & 2 & -1 & 0 \\ 2 & 4 & 0 & 4\end{array}\right]$ What are the dimensions of matrix $ E$ ?
Explanation: The first dimension is the number of rows in the matrix. How many rows does $ E$ have? The second dimension is the number of columns in the matrix. How many columns does $ E$ have? So, $ E$ is a 3 $\times$ 4 matrix.